Genetic improvement of heavy metal tolerance in plants by transfer of the yeast metallothionein gene (CUP1)

Cauliflower (Brassica oleracea var. botrytis) tolerates treatment with 25 mu M CdCl2 for eight days, but is killed by that with a 50 mu M concentration. However, even 15 mu M CdCl2 is toxic in the presence of 1 mM L-buthionine sulfoximine (BSO), suggesting the presence of a Cd-inducible phytochelatin and its involvement in Cd-tolerance in cauliflower. To develop heavy metal-tolerant transgenic plants, we ligated the structural gene of yeast metallothionein gene (CUP1) downstream of CaMV35S promoter and introduced the fused gene into cauliflower. A Cd-tolerant transgenic cauliflower was selected, which grew well in the presence of 400 mu M or less Cd, whereas the non-transformed cauliflower tolerated only up to 25 mu M Cd. The transgenic cauliflower accumulated more Cd, especially in the upper leaves, than the non-transformed plant. In conclusion, by transfer of the yeast metallothionein gene into cauliflower increased Cd-tolerance and CD-accumulating ability can be conferred to the plant.